Certain copy-protection schemes for optical discs, e.g. CDROM, DVD or blue-ray disc, check if a special feature, a so-called “signature”, which can not be duplicated onto optical recordable media, is present on the optical disc. Such a signature and a corresponding method for verifying the signature are disclosed for example in WO 03/054878 A1 or in EP1672631A1. A computer program is only allowed to execute if the signature is present. Copy-protection software is looking for such a signature on a target storage medium, which should be e.g. an original optical disc, and which is expected to be placed in a target storage drive, e.g. an optical disc drive. An operating system of a computer system presents a storage drive together with a storage medium as a storage volume. Other examples for such storage volumes might be provided by a USB-Stick (semiconductor memory with a USB interface), a floppy drive with a floppy disk, a memory card in a card-reader or partitions on hard disks. The wording “target storage medium”, “target storage drive” and “target storage volume” is used throughout this description for the corresponding storage medium, storage drive and storage volume on which the certain data is expected to be found by the copy-protection software. Typically, the copy-protection software is checking, whether the signature is present on the target storage volume.
Emulation software intercepts the communication between the copy protection software and the optical disc drive, and manipulates the data and/or access timing information to insert false signature information. Emulation software can achieve this by presenting a virtual storage medium such as a disc image mounted on a virtual drive as a virtual storage volume to the copy protection software, while the disc image is actually stored on a hard disk drive (HDD).
Such virtual storage volumes with disc images of floppy disks, optical discs etc. are useful in certain circumstances, i.e.:                They enable users to avoid constantly changing discs.        They enable users to carry large disc libraries without the physical burden of the discs.        They can make a disc accessible to users on a network, which is very practical when it is impossible to distribute the discs to all of the users of the network.        
However, in cases where the content of a copy protected optical disc is stored as a disc image on the hard disk and presented to a copy protection software (also called control logic), copy-protection schemes may be circumvented by malicious virtual drive software, which not only provides access to the content but also to the signature. The copy-protection software is not aware of the fact that the target storage volume, on which the signature is found, is not the original optical disc in an optical disc drive, but is a disc image on the hard disk drive. The original disc might be redistributed to other user(s), and the copy on the hard disk drive might be in fact an unauthorized copy.
Known methods to identify a virtual storage volume depend either on system-level software (“device drivers”) or have become ineffective. Such previous methods may include separately or in combination:                requiring the target disc as target storage medium to be played in a non-SCSI (Small Computer System Interface)-drive,        querying and blacklisting a disc drive adapter's information,        querying uncommon properties of the disc drive, which are not emulated/provided by the virtual drive software, e.g measuring the interval between a start and a stop command or measuring random access time.        
A further possibility to protect data content within protected areas on a target optical carrier against unauthorized reading and/or copying with a computer is disclosed in WO 2004/088658 A1. The disclosed method comprises steps of determining whether a target optical record carrier or a non-target optical record carrier is inserted into a drive of the computer, and—if a target optical record carrier is inserted into the drive of the computer—modifying read requests to the protected data areas so that no data is read or the read data is useless, and/or—modifying write commands in respect to the data within the protected data areas to a recordable carrier or other storage so that the written data is useless.
It is an object of the present invention to provide a method for detecting a virtual storage volume which is difficult to circumvent and which provides an effective way to discover whether a virtual storage volume is used in order to fake or otherwise give the impression that the presence of an original storage medium in a corresponding drive,
It is a further object of the present invention to provide a control logic for detecting a virtual storage volume which enables an easy and efficient detection of such virtual storage volume, when used on a computer system to provide measures against unauthorized copying of protected software applications or data.
It is a further object of the present invention to provide a system for detecting a virtual storage volume which enables an easy and efficient detection of such virtual storage volume, which are present on such a system.